While digging for more on this, I found a product description from the Fine Sporting Collectibles website for a stock item they had but has been sold.

" A nickel silver ventometer for making small alterations to the back sight of a rifle. Made by W.J. Jeffery & Co. London and were used with the Martin Henry and Lee Metford and Lee Enfield. "

Haven't found the orig patent documents yet, maybe later.
At this point my curiosity has been satisfied!

Cheers
Tinker